Offenders having both mental illness and chemical abuse (MICA) disorders are a population of interest, in part because their special needs place exceptional demands on criminal justice and treatment systems, as well as on individuals and families. The proposed study examines the crucial point of transition from prison to the community, where continued treatment for offenders is generally considered necessary to sustain gains made by prison treatment efforts, and to achieve successful outcomes. On their release from prison, male offenders with MICA disorders who elect to participate in this study (N = 332), will be placed in either the experimental condition, (E) Re-entry Modified Therapeutic Community (Re-entry MTC) or the control condition, (C) Parole Supervision and Case Management currently provided, using a randomized block assignment procedure. The research employs a prospective, longitudinal, repeated measures assessment with five data collection points: baseline (Time 1, or T1) corresponding to entry into the Community Corrections facility and at 3 (T2), 6 (T3), 12 (T4), and 18 (T5) months post-baseline. The major study hypothesis is that the E condition (compared to the C condition) will produce significantly greater improvement in the presenting problems of the study participants, as measured by substance use, mental health symptoms, and criminal activities. This project will advance scientific knowledge through a controlled study of the effectiveness of the MTC model, with demonstrated success in community settings, as a re-entry strategy for offenders with MICA disorders, thereby expanding the range of treatment models available to such clients in the community. In addition, the study will examine the degree to which prior prison treatment moderates the effectiveness of the Re-entry MTC, or the extent to which positive outcomes are independent of the type of treatment received during the prior incarceration. This distinction will inform program planning by establishing the value of MTC treatment in prison plus MTC during re-entry versus MTC re-entry treatment alone. Finally, the study tests a specific hypothesis about the degree to which the effectiveness of Re-entry MTC treatment is mediated by client progress during reentry, which will increase our understanding of the relationship between progress in treatment and post-treatment outcomes for offenders with MICA disorders.